This invention relates generally to active pixel photosensors. In particular, it relates to a stacked multiple active pixel photo sensor that includes independent electrical connections to each photosensor, allowing multiple color detection.
An array of photo pixel sensors detect the intensity of light received by the photo pixel sensors. The photo pixel sensors typically generate electronic signals that have amplitudes that are proportionate to the intensity of the light received by the photo pixel sensors. The photo pixel sensors can convert an optical image into a set of electronic signals. The electronic signals may represent intensities of colors of light received by the photo pixel sensors. The electronic signals can be conditioned and sampled to allow image processing.
Integration of the photo pixel sensors with signal processing circuitry is becoming more important because integration enables miniaturization and simplification of imaging systems. Integration of photo pixel sensors along with analog and digital signal processing circuitry allows electronic imaging systems to be low cost, compact and require low power.
Historically, photo pixel sensors have predominantly been charged coupled devices (CCDs). CCDs are relatively small and can provide a high-fill factor. However, CCDs are very difficult to integrate with digital and analog circuitry. Further, CCDs dissipate large amounts of power and suffer from image smearing problems.
An alternative to CCD sensors are active pixel sensors. Active pixel sensors can be fabricated using standard CMOS processes. Therefore, active pixel sensors can easily be integrated with digital and analog signal processing circuitry. Further, CMOS circuits dissipate small amounts of power.
FIG. 1 shows a prior art array of active pixel sensors. An array of sensors 12 are formed over a substrate 10. An array of color filters 14 is formed over the array of sensors 12. Light passes through the color filters 14 and is received by the array of sensors 12. The sensors 12 typically conduct charge at a rate that is proportional to the intensity of the light received by the sensors 12. Circuitry located on the substrate 10 provides determination of the amount of charge conducted by the sensors 12. Therefore, the sensors 12 provide detection of the intensity of the received light.
The array of color filters 14 includes filters which pass different wavelengths of light. For example, the array of color filters 14 can include blue light, green light and red light filters. The blue light filters only passes blue light, the green light filters only passes green light and the red light filters only pass red light. Generally, each sensor of the array of sensors 12 corresponds with a single color filter of the array of color filters 14. Color detection can be obtained by knowing which sensor corresponds with which type of color filter.
The active pixel sensor array of FIG. 1 is inefficient because up to 70% of the photons within the received light are lost during the filtering process. That is, the color filters 14 attenuate the intensity of the light received by the array of sensors 12. Removing the color filters 14 increases the intensity of light received by the array of sensors 12. As a result, the color filters 14 reduce the signal to noise ratio of the electronic signals generated by the array of sensors 12.
The active pixel sensor array of FIG. 1 requires demosaicing. Each sensor of the array of sensors 12 detects the intensity of a particular color of light. Each sensor is physically displaced from all of the other sensors of the array of sensors 12. Therefore, special image processing (demosaicing) is required for determination of a representation of the color intensity received by the array of sensors 12 at each particular pixel location.
It is desirable to have an array of active pixel sensors which provide efficient absorption of photons within light received by the array of active pixel sensors, and be able to detect the color of received light. It is also desirable that the array of active pixel sensors be manufacturable without an array of color filters and not require demosaicing.
The present invention is a color detection active pixel sensor which provides efficient absorption of photons of light received by the color active detection pixel sensor while providing detection of the color of the received light. The color detection is accomplished without color filters and does not require demosaicing.
A first embodiment of the invention includes a multiple-photosensor structure. The multiple-photosensor structure includes a substrate. A first photosensor is formed adjacent to the substrate. A first pixel electrode of the first photosensor is electrically connected to the substrate. A first transparent conductive layer is formed adjacent to the first photosensor. The first transparent conductive layer electrically connects a first outer electrode of the first photosensor to the substrate. A second photosensor is adjacent to the first transparent conductive layer. A second pixel electrode of the second photosensor is electrically connected to the substrate through the first transparent conductive layer. A second transparent conductive layer is adjacent to the second photosensor. The second transparent conductive layer electrically connects a second outer electrode of the second photosensor to the substrate.
A second embodiment of the invention is similar to the first embodiment. The second embodiment includes a third photosensor formed adjacent to the second transparent conductive layer. A third pixel electrode of the third photosensor is electrically connected to the substrate through the second transparent conductive layer. A third transparent conductive layer is formed adjacent to the third photosensor. The third transparent conductive layer electrically connects a third outer electrode of the third photosensor to the substrate.
A third embodiment of the invention is similar to the first embodiment. The third embodiment includes the first photosensor detecting a first range of wavelengths of light.
A fourth embodiment of the invention is similar to the first embodiment. The fourth embodiment includes the second photosensor detecting a second range of wavelengths of light.
A fifth embodiment of the invention is similar to the second embodiment. The fifth embodiment includes the third photosensor detecting a third range of wavelengths of light.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.